How Do You Know When to Size Up Baby's Cloth Diapers?
One of the most common questions cloth diapering parents ask is when to size up their baby’s cloth diapers. With disposable diapers, you simply follow the printed weight range on the package. Cloth diapers work a little differently. Fit depends on your baby’s shape, growth pattern, absorption needs, and comfort. That means the best time to size up is not just about weight. It is about watching for clear signs of a good fit on your baby and learning how cloth diapers should look and behave at each stage. Look for these 8 signs: Red marks on thighs, leg gaps, leaks that are not caused by absorbency, diaper sitting low on baby's back, waist snaps are fully open, difficulty getting diapers on, insert not laying flat, baby has outgrown absorbency and needs more room.
Sizing up at the right time prevents leaks, protects your baby’s skin and keeps your diapering routine stress-free. In this guide, we will walk you through the most reliable signs your baby is ready to size up a cloth diaper, the common mistakes many parents make, and how to achieve the perfect fit, whether you use AIOs, pockets, or diaper covers.
Understanding How Cloth Diaper Sizing Works
Cloth diapers are adjustable by nature, but they are not one-size-fits-all in every moment. Even one-size cloth diapers require occasional adjustments to the rise snaps, waist snaps, and sometimes the insert setup. Babies grow in spurts, experience changes in chubbiness, and develop different mobility needs. Because of this, the best time to size up your cloth diaper depends on your baby’s body, not their age or weight. And this is exactly why Lighthouse Kids Company Cloth Diapers come in two sizes, so you have the perfect fit every single time.
Most modern cloth diapers, including Lighthouse Kids Company AIO, Pocket, and AI2 systems, use a snap-down rise that allows the diaper to fit everything from small newborns to large toddlers. However, if the diaper is set too small or too large, you may experience leaks, red marks or gaps. When your rise setting no longer fits comfortably, it is time to size up.
The Most Common Signs Your Baby Needs to Size Up Cloth Diapers
Here are the clearest and most reliable signs that it is time to size up your baby’s cloth diapers.
1. Red Marks on the Thighs or Waist
A small indentation from elastic is normal, just like sock marks. What you do not want to see are deep red ridges or irritated skin. If your baby has strong elastic marks that do not fade quickly, it often means the diaper is too tight.
This can happen when:
- Your baby has gained weight
- Your baby has chunkier thighs
- Your child is sitting or crawling more, causing more pressure on the elastic
- The rise is too low, pulling the leg openings inward
Sizing up the rise setting or moving to a larger waist snap setting usually fixes this problem.
2. Leg Gaps That Cause Leaks
If you notice gaps around your baby’s legs, especially when they move, kick, or crawl, the diaper may be set too large or too small. Leg gaps are responsible for most leaks in cloth diapers, particularly with runny poop.
If the elastic does not hug the thigh gently or if you can see inside the diaper when your baby moves, size up the rise setting or check whether the waist needs adjustment. Age changes how fat is distributed on the thighs, so young infants may be on a smaller rise while older babies may need the rise unsnapped as they grow taller.
3. Frequent Leaks That Are Not Caused by Absorbency
If your cloth diaper suddenly begins leaking and you know the diaper is not fully saturated, the fit may be the issue. A good fit prevents compression leaks and side leaks. If leaks begin happening out of nowhere, double-check:
- Leg gaps
- Tummy gaps
- Rise setting
- Wing position
- Insert placement
If everything seems to be snug but leaks continue, your baby may need a roomier rise setting to accommodate movement and absorbency layers.
4. The Diaper Sits Too Low on the Baby’s Back
A cloth diaper should sit at or slightly below the natural waistline. If the back panel begins slipping downward or the top edge looks much lower than before, your baby may need a higher rise. Babies who start to crawl or walk often gain height quickly and need more vertical room in their diaper. If the back panel barely covers the bum or moves down while active, it is time to size up.
5. The Waist Snaps Are Almost Fully Open
When your waist snaps reach the very last snap or only one snap remains before the diaper cannot close, this is a reliable sign that your baby is outgrowing the current setting. Babies grow outward in the tummy area as they develop better core muscles, eat more solids, and begin toddling. If you are maxed out on waist snaps, size up.
6. Difficulty Getting the Diaper On
If you find yourself pulling, stretching or struggling to get the diaper snug enough without causing red marks, your baby may have grown out of the setting. Cloth diapers should be easy to put on. You should not have to tug or force the snaps closed. As soon as the fit begins requiring extra effort, try increasing the rise or adjusting the waist outward.
7. The Insert Is Not Lying Flat Inside the Diaper
If the insert bunches, curls, or bulges because the diaper shell is too small, your baby may need a larger rise setting. Inserts should lie flat inside the diaper to prevent pressure leaks and discomfort. A diaper that is too small cannot accommodate absorbency without bunching. Note: Some cloth diaper companies use subpar materials for their inserts, which may cause excessive curling at the edges. If the inner absorbency cannot sit flat, size up.
If you have inserts that are extremely "bacony" that means they combined two materials that shrink at different rates. Some curling is normal; extreme curling means the wrong materials were chosen for the inserts.
8. Baby Has Outgrown the Absorbency and Needs More Room
As babies grow and begin sleeping longer stretches, drinking more, and eating solids, they need additional absorbency. Sometimes the diaper shell fits fine, but the increased bulk of the added boosters makes the diaper too tight. This is very common at night.
If you add boosters and the diaper suddenly looks tight, difficult to snap or uncomfortable, you may need to size up so the baby has room for nighttime absorbency.
How to Adjust Rise Settings the Right Way
Most parents start with a smaller rise setting during infancy, then gradually size up as their baby grows taller. Here is a general guideline for rise sizing:
- Lowest rise setting: newborns to about 10 to 12 pounds
- Middle rise: older infants who sit, roll, and crawl
- Fully open rise: toddlers and early potty trainers
Your baby may move between these stages quickly or slowly, depending on growth. Always trust your baby’s fit over the numbers.
To check if the rise is correct:
- Pull the diaper up between baby’s legs.
- Check that the rise seam sits flush against the groin.
- Make sure no fabric is bunched or folding awkwardly.
- Look for leg gaps or tightness.
- If you see bunching, pulling, sagging or gaps, adjust the rise higher or lower.
Fit Differences Between AIO, Pocket, and AI2 Cloth Diapers
Different diaper styles fit differently. Understanding these differences helps you size up correctly.
All-In-One (AIO) Cloth Diapers
AIO diapers have absorbency sewn in, so the fit depends heavily on having enough room around the legs and waist. As babies grow taller, you will often size up the rise sooner in AIOs than in pocket diapers because the interior layers take up space.
Babies who sleep longer or wet heavily may require a larger rise to accommodate boosters.
Pocket Diapers
Pocket diapers are adjustable and allow you to choose the absorbency level. Because inserts go in the pocket, the outer shell may fit longer before needing to size up. If the pocket is difficult to stuff or the inserts curl inside, this is a sign you need to increase the rise setting.
AI2 (All In Two) or Diaper Covers
The same rules applies to diaper covers or AI2, if you see deep red marks around the thighs or gaps around the legs, size up the rise or switch to the next setting.
Why Sizing Up Matters
Sizing up is not just about comfort. It affects:
- Leak prevention
- Skin health
- Mobility
- Absorbency capacity
- Restful sleep
- Diaper lifespan
A diaper that is too tight causes pressure leaks. A diaper that is too loose causes side leaks. Proper fit keeps the absorbency exactly where it needs to be and prevents irritation.
Many families discover that sizing up fixes 90 percent of common cloth diaper issues such as frequent leaks, red marks, and discomfort.
When NOT to Size Up
Sometimes parents size up too early, thinking gaps or leaks mean the diaper is too small when actually it is too big.
Keep the diaper on a smaller rise if:
- The diaper is sagging
- The insert is shifting or bunching
- You can see inside the diaper when the baby moves
- Leg gaps are present even when tightened
- The back panel is creeping too high up the waist
A diaper that is too big leaks more than one that is too small. Always check the rise setting first before moving to the next size up.
How Often Will Babies Size Up Cloth Diapers
Babies size up at different rates. Some stay on one rise for months. Others move through three rise settings in just a few weeks. Here is a general timeline:
- 0 to 3 months: multiple size adjustments
- 3 to 9 months: stable for longer
- 9 to 18 months: often require a larger rise as height increases
- 18 months to potty learning: diapers usually stay on the largest rise
Toddlers with tall bodies or fuller thighs may need the largest rise sooner than expected.
Final Thoughts: Trust the Signs, Not the Weight Chart
The best guide for when to size up a cloth diaper is your baby. Watch for red marks, gaps, leaks, difficulty closing snaps, or changes in absorbency needs. Once you learn how cloth diapers should fit, sizing up becomes simple and stress-free.
Cloth diapering is flexible, adjustable, and designed to follow your baby’s growth. When you size up at the right moment, everything becomes easier. Your diapers last longer, your baby stays comfortable, and your diapering routine stays smooth and reliable.
